Rhododendron plant named ‘HoldenRhodo221’

ABSTRACT

A new cultivar of hybrid Rhododendron plant named ‘HoldenRhodo221’ that is characterized by its resistance to root rot caused by Phytophthora cinnamomi, its cold hardiness (plant and flower buds) at least to U.S.D.A. Zone 5a, its flowers that are red to dark pink in color with strong marginal undulation, its profuse and consistent flowering, its compact plant habit, its foliage that is dark in color and glossy, and its good growth in full sun in unamended sand and gravel loam soils, up to at least pH 6.2.

Botanical classification: Rhododendron hybrida.

Cultivar designation: ‘HoldenRhodo221’.

BACKGROUND OF THE INVENTION

The present invention relates to a new and distinct cultivar ofRhododendron plant of hybrid origin, botanically known as Rhododendron‘HoldenRhodo221’ and will be referred to hereafter by its cultivar name,‘HoldenRhodo221’. ‘HoldenRhodo221’ is a new cultivar of Rhododendronshrub grown for use as a landscape plant.

The new cultivar arose from a controlled breeding program by theInventor in Madison, Ohio with the goal of developing new cultivars ofRhododendron with good resistance to root rot caused by Phytophthoracinnamomi, cold hardiness (plant and flower buds), and compact growthhabits with diversity in flower forms and colors.

The new cultivar was derived from a cross made by the Inventor in May of2003 between Rhododendron ‘Ingrid Mehlquist’ (not patented) as thefemale parent, and Rhododendron ‘Pride's Early Red’ (not patented) asthe male parent. The Inventor selected ‘HoldenRhodo221’ as a singleunique plant amongst the seedlings that resulted from the above cross inMay of 2010.

Asexual propagation of the new cultivar was first accomplished bysemi-hardwood stem cuttings in Madison, Ohio, in fall of 2010 by theInventor. Asexual propagation by semi-hardwood stem cuttings and tissueculture utilizing meristematic tissue has determined that thecharacteristics of the new cultivar are stable and are reproduced trueto type in successive generations.

SUMMARY OF THE INVENTION

The following traits have been repeatedly observed and represent thecharacteristics ‘HoldenRhodo221’. These attributes in combinationdistinguish ‘HoldenRhodo221’ as a new and distinct cultivar ofRhododendron.

-   1. ‘HoldenRhodo221’ exhibits resistance to root rot caused by    Phytophthora cinnamomi.-   2. ‘HoldenRhodo221’ exhibits cold hardiness (plant and flower buds)    at least to U.S.D.A. Zone 5a.-   3. ‘HoldenRhodo221’ exhibits flowers that are red to dark pink in    color with strong marginal undulation.-   4. ‘HoldenRhodo221’ exhibits profuse and consistent flowering.-   5. ‘HoldenRhodo221’ exhibits a compact plant habit.-   6. ‘HoldenRhodo221’ exhibits foliage that is dark in color and    glossy.-   7. ‘HoldenRhodo221’ exhibits good growth in full sun in unamended    sand and gravel loam soils, up to at least pH 6.2.

The female parent of ‘HoldenRhodo221’ differs from ‘HoldenRhodo221’ inhaving inflorescences that are smaller in size, flower buds that arepink in color and change to white as the flowers open, leaves that aredarker in color, lower leaf surfaces that are densely covered with browncolored indumentum, and flowers that do not produce anthers. The maleparent of ‘HoldenRhodo221’ differs from ‘HoldenRhodo221’ in havinggreater susceptibility to root rot caused by Phytophthora cinnamomi, aless compact plant habit, flowers with margins that lack undulations,and an earlier blooming period. ‘HoldenRhodo221’ can also be mostclosely compared to the Rhododendron cultivars ‘Nova Zembla’ (notpatented) and ‘Holden’ (not patented). ‘Nova Zembla’ is similar to‘HoldenRhodo221’ in having red to dark pink colored flowers and in beingcold hardy to U.S.D.A. Zone 5. ‘Nova Zembla’ differs from‘HoldenRhodo221’ in having flowers that are less red in color, a lesscompact plant habit, leaves that are more twisted, and moresusceptibility to root rot caused by Phytophthora cinnamomi. ‘Holden’ issimilar to ‘HoldenRhodo221’ in having a compact plant habit and in beingcold hardy to U.S.D.A. Zone 5. ‘Holden’ differs from ‘HoldenRhodo221’ inhaving flowers that are more pink in color with a more prominent nectarguide on the dorsal petal, more susceptibility to root rot caused byPhytophthora cinnamomi, and plant and flower bud cold hardiness toU.S.D.A. Zone 5b but not 5a.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying color photographs illustrate the overall appearance anddistinct characteristics of the new Rhododendron. The plant in thephotograph is 6 years in age as grown outdoors in Madison, Ohio.

The photograph in FIG. 1 provides a view of the plant habit of‘HoldenRhodo221’ in bloom.

The photograph in FIG. 2 provides a close-up view of the inflorescencesof ‘HoldenRhodo221’.

The colors in the photographs are as close as possible with the digitalphotography and printing techniques utilized and the color codes in thedetailed botanical description accurately describe the new Rhododendron.

DETAILED BOTANICAL DESCRIPTION OF THE PLANT

The following is a detailed description of 11-year-old plants of the newcultivar as grown outdoors in an evaluation garden in Madison, Ohio. Thephenotype of the new cultivar may vary with variations in environmental,climatic, and cultural conditions, as it has not been tested under allpossible environmental conditions. The color determination is inaccordance with The 1995 Colour Chart of The Royal HorticulturalSociety, London, England, except where general color terms of ordinarydictionary significance are used.

-   General characteristics:    -   -   Blooming period.—2 to 3 weeks, weather dependent, typically            in mid-late May in Madison, Ohio.        -   Plant type.—Evergreen shrub.        -   Plant habit.—Rounded, compact, and densely branched.        -   Height and spread.—Reaches 52 m in height and 60 cm in width            after 11 years in the landscape.        -   Cold hardiness.—Plant is hardy to at least U.S.D.A. Zone 5a,            flower buds are resistant to cold damage when exposed to            temperatures of −15 F, possibly colder.        -   Diseases and pests.—Observed to be resistant to root rot            caused by Phytophthora cinnamomi under field conditions, no            resistance or susceptibility to pests and other diseases has            been observed.        -   Root description.—Fibrous and near 165A in color.        -   Propagation.—Tissue culture (preferred) or semi-hardwood            stem cuttings.        -   Growth rate.—Moderate.        -   Root development.—8 to 10 weeks for root initiation and 2            years to produce a plant with flower buds from a rooted            cutting in a one-gallon container.-   Stem description:    -   -   Shape.—Rounded.        -   Stem color.—Young, new growth; 143C, mature; 144B, old stems            and wood; 164B and 165C, striations of 199A, 199C, 199D, and            201D.        -   Stem size.—Main trunk; 27 cm in height, 3.5 cm in width (2            cm from soil level), lateral stems; 35.7 cm in length, 1.3            cm in width, current season growth; average of 7 cm in            length and 5 mm in width.        -   Stem surface.—Young; is slightly rough to the touch, lightly            pubescent with hairs an average of 1 mm in length, 158D in            color, mature stems become glabrous, older stems and wood;            somewhat rough, dull, glabrous, and occasionally            exfoliating.        -   Stem aspect.—Stems emerge from plant at various angles,            typically approximately 45° from main stem.        -   Stem strength.—Strong.        -   Branching.—Densely branched.-   Foliage description:    -   -   Leaf shape.—Elliptic to obovate.        -   Leaf division.—Simple.        -   Leaf base.—Cuneate.        -   Leaf apex.—Ovate to slightly acute.        -   Leaf venation.—Pinnate, upper surface midrib; 144B in color            with lateral vein color matching or nearly matching midrib            coloration, lower surface midrib; 145C, lateral veins near            145B.        -   Leaf margins.—Entire with strong undulation.        -   Leaf attachment.—Petiolate.        -   Leaf arrangement.—Alternate to nearly whorled.        -   Leaf internode length.—Ranges from 1 mm to 7.3 cm becoming            progressively smaller from base to apex of shoot, 1 mm to 2            mm in whorl of foliage at shoot apex.        -   Leaf orientation.—Held mostly parallel to the ground, some            angled 30° above or below parallel.        -   Leaf aspect.—Usually flat but occasionally leaves cup            downward.        -   Leaf surface.—Upper surface; smooth, glabrous, lustrous with            a thick texture, moderately covered with hairs, <1 mm in            length and 159B in color, lower surface; smooth, dull, and            glabrous except prominent mid-rib with occasional short            cilia <0.5 mm in length.        -   Leaf color.—Young leaves upper surface; 137B in color, young            leaves lower surface; a blend of 145A and 146D, mature            leaves upper surface; nearest 139A, lower surface 146B.        -   Leaf size.—Ranging between 7 cm to 12.5 cm in length and 2.3            cm to 5.0 cm in width.        -   Leaf quantity.—An average of 9 leaves per current season            shoot.        -   Petioles.—Average of 2.5 cm in length and 3 mm in width,            144B in color, smooth texture.-   Flower description:    -   -   Inflorescence type.—Raceme.        -   Lastingness of flowers.—Individual flowers last several            days, total duration of bloom ranges from 2 to 3 weeks,            self-cleaning.        -   Inflorescence size.—Average of 7.5 cm in height and 11.2 cm            in width.        -   Flower size.—An average of 3.8 cm in depth and 6.4 cm in            width.        -   Flower fragrance.—Not noticeably fragrant.        -   Flower shape.—Broad, with partially fused corolla.        -   Flower number.—Ranges from 11 to 23 per inflorescence.        -   Flower aspect.—Outward.        -   Flower bud.—Resting (winter buds); typically 1 per terminal            branch (can be none or more than one), an average of 1.3 cm            in length and 6 mm in diameter as a resting bud, 145A in            color with margins and ridges a blend of 175A and 176A,            balloon stage; obovate to elliptic in shape, round in            cross-section, pointed apex, 2.5 cm in length and diameter,            54A in color at base and a blend of 53A and 60A near            terminal end.        -   Flower attachment.—Pedicellate.        -   Petal number.—5, partially fused.        -   Petal shape.—Ovate to elliptic.        -   Petal color.—Opening and fully open upper surface; margins            63A, center 63D, speckled with 66C around nectar guides,            fading; margins 66D, center a blend of 63A to 63B, opening            and fully open lower surface; margins 63A, center 63B to            63C, speckled with 66C around nectar guides, fading; a blend            of 63A to 63B and 65A.        -   Petal surface.—Both surfaces smooth and glabrous.        -   Petal margins.—Inconsistently crenate, undulate.        -   Petal apex.—Acuminate to obtuse, often recurved and keeled.        -   Petal base.—Fused.        -   Petal size.—An average of 4.4 cm in length, 3.2 cm in width.        -   Sepal number.—5.        -   Sepal margin.—Entire.        -   Sepal size.—Average of 1 mm in length and width.        -   Sepal apex.—Rounded to flat.        -   Sepal base.—Fused.        -   Sepal color.—143C.        -   Calyx.—Shallowly cup-shaped an average of 1 mm in length and            diameter, with individual sepals separated by rounded            sinuses.        -   Peduncle.—An average of 3.2 cm in height and 6 mm in            diameter, 144B in color.        -   Pedicels.—An average of 2.2 cm in length 2 mm in diameter,            144B in color, surface is glabrous to slightly pubescent.-   Reproductive organs:    -   -   Gynoecium.—1 Pistil, stigma; round in shape, 59A in color, 1            to 2 mm in diameter, style average 3.4 cm in length, ovary            73D in color.        -   Androecium.—Stamens; typically 10 to 11, anthers; oblong to            elliptic in shape, average of 2.5 mm in length, 1 mm in            width, 4B in color, filaments; average of 1.9 cm in length,            63C in color, covered in fine white hairs especially near            base; pollen present but too small to measure.        -   Fruit/seeds.—Dehiscent, 5 to 6 valved capsule, varying in            length and width depending on pollination, color; 165A and            166A with some overtones of 201A in late summer, tends to            produce low amounts of seed as a female parent and seed            measurements are unavailable.

It is claimed:
 1. A new and distinct cultivar of Rhododendron plantnamed ‘HoldenRhodo221’ as herein illustrated and described.